Tubular steel structures -- Deterioration

The corrosion propagation stage of D-CRP (types F and C) was tested under
immersion in water, high humidity, and covered with wet sand. The half-cell potential,
linear polarization test, and electrochemical impedance spectroscopy measurements were
performed. Selected specimens were terminated after 300 days of exposure and visually
inspected. Based on corrosion potential measurements obtained during the corrosion
propagation observation, and calculated corrosion rate based on LPR measurements: all
specimens were actively corroding. Additionally, EIS-Rc values were calculated for FS,
CS and CH specimens. The Rc_EIS were generally greater than Rc_LPR values. EIS
spectra for CI and FI specimens usually included mass transport limitations, as these
specimens were immersed. Both type of specimens immersed in water (FI and CI), appeared to have higher corrosion rate based on LPR-Rc. However, upon autopsy
it was revealed that a more modest amount of corrosion occurred on the reinforcing steel
of FI and CI terminated specimens.

Instrumented dry-cast reinforced concrete pipe (DC-RCP) specimens in which
corrosion of the reinforcing steel had initiated were selected to accelerate the corrosion.
Type C and type F DC-RCP were used. An anodic current density of various magnitudes
(0.5 μA/cm2, 1 μA/cm2 and 2.5 μA/cm2) was applied during the corrosion propagation
stage. The specimens were placed in high humidity and selected specimens were later
covered with wet sand. Selected specimens were terminated for visual examination and
gravimetric analysis. Typically, the reinforcement potentials during the accelerated
corrosion period were more negative for F specimens compared to C specimens. The C
specimens experienced ~2× more corrosion than the F specimens. The accumulated
corrosion products did not cause cracks. A method was developed that allows for modest
corrosion acceleration during the corrosion propagation stage of DC-RCP.